Gastric Digestion Model Research Articles

Comparing gastric emptying of cellulose nanocrystals with sodium alginate and pectin using a dynamic in vitro stomach model

Cellulose nanocrystals (CNC) are increasingly recognized for their potential in various applications, including packaging, cosmetics, and biomedical engineering. Due to their gelation properties influenced by pH and ionic strength, CNC could impact gastric emptying and satiety, beneficial for managing obesity and diabetes. This study investigated the gastric emptying of CNC (4 % and 8 %, w/w) in comparison with sodium alginate (2 %, w/w) and pectin (2 %, w/w), exploring the effect of divalent cations (Ca2+ and Mg2+) using a dynamic gastric digestion model. CNC, in the presence of Ca2+ and Mg2+, formed a high-viscosity gel network under gastric conditions, leading to delayed gastric emptying. While alginate formed strong gels with Ca2+, it did not significantly delay gastric emptying due to the poor water-holding capacity of its gel network. Pectin showed minimal impact on gastric emptying. Among the treatments, the half-time (t1/2) of gastric emptying for 8 % CNC with Ca2+ was observed to be the longest at 215.4 ± 23.7 min, compared to the shortest times observed with pectin at 15.1 ± 1.4 min. The results suggest that different mechanisms are involved in the gastric emptying effect of different dietary fibers, and CNC is more effective than alginate and pectin assisting in promoting gastric retention and aiding in the management of body weight. This study also introduced a novel application of the dynamic gastric digestion model for estimating digestion energy expenditure, providing insights into the impact of dietary fiber on gastric emptying and satiety enhancement.

An<em> in-vitro</em> gastric digestion model with peristalsis function for the analysis of the food gastric digestion

In vitro models of the human stomach offer a robust platform to explore the physicochemical processes during gastric digestion. In Sri Lanka, limited research has been conducted on the digestion behavior of diverse food structures using in vitro digestion models. This study aims to create a custom-built in vitro gastric digestion model, specifically designed for Sri Lankan laboratories to analyze food digestion in a simulated stomach environment. The physical model comprises a butyl rubber chamber simulating the stomach, 4 nylon rollers with 2 rubber belts, driven by geared motors, and 6 nylon pulleys, creating continuous contractions of the rubber chamber. The model simulates the peristaltic movements of the stomach wall, with contraction waves occurring at a frequency of approximately 3 cycles per minute, mimicking in vivo peristaltic movement. Gastric sieving, secretion, emptying, and temperature control mechanisms are employed to recreate dynamic gastrointestinal conditions. A polyester mesh bag with a pore size of 1.5 mm replicates the gastric sieving function, while manual gastric emptying is performed. Gastric juice is secreted into the chamber at a rate of 2.5 mL/min using a programmed peristaltic pump, and an automated temperature control system maintains the ambient temperature at 37 °C. In conclusion, this developed gastric device serves as an effective tool for studying the gastric digestion of various food structures within a simulated stomach environment.

Использование плазмолизированных дрожжей для инкапсуляции и повышения биодоступности растительных антиоксидантов

Abstract. The yeast Saccharomyces cerevisiae is widely used in many fermentative processes of food production. At the same time, the spent yeast biomass obtained after production processes generates significant amounts of waste. Thus, in the brewing industry residual brewer's yeast is the second largest volume of waste, which is about 3% of the volume of brewed beer. Utilization of these wastes is rather complicated and requires additional costs from the enterprises. Under these conditions, the directions of additional utilization of spent yeast mass are of high interest. One of such directions can be the use of plasmolysis of spent yeast and its further use for encapsulation of biologically active substances. Among biologically active compounds, plant polyphenols – substances with pronounced antioxidant properties – occupy an important place. Scientific novelty. This study examines dihydroquercetin, rutin and curcumin in their original and nanostructured forms. For these compounds an extensive list of pharmacological properties such as anti-inflammatory, antioxidant, capillaroprotective and others has been established. At the same time, these compounds are characterized by a low level of bioavailability. The purpose of the study was to investigate the possibility of using spent, plasmolysed cells of brewer's yeast Saccharomyces to encapsulate plant polyphenols: dihydroquercetin, rutin and curcumin, and to evaluate the effect of such an approach on the bioavailability of biologically active substances in an in vitro digestion model. Results. As a result of these studies, it was found that plasmolysed yeast cells are able to act as a “delivery system” of plant antioxidants. Using the proposed approaches, it is possible to achieve an encapsulation efficiency of approximately 57–64 %, provided that the polyphenols are ultrasonically nanostructured beforehand. Analysis of the potential bioavailability of encapsulated forms of plant antioxidants in an in vitro gastric digestion model showed that the technology of encapsulation into yeast cells allowed to ensure the preservation of plant antioxidants about 80 %. In comparison with the initial forms of biologically active substances, encapsulation allowed to provide an increase in bioavailability by about 30–40 %.

Characterizations of emulsion gel formed with the mixture of whey and soy protein and its protein digestion under in vitro gastric conditions

Partially replacing animal proteins with plant proteins to develop new products has much attention. To get knowledge of their application in emulsion gels, heat-induced composite protein emulsion gels were fabricated using the mixtures of whey protein isolate (WPI) and soy protein isolate (SPI) with the final total protein concentration of 10% (w/w). The water holding capacity (WHC), mechanical and rheological properties and microstructure of mixed protein emulsion gels prepared at different WPI to SPI ratios (100:0, 90:10, 70:30, 50:50, 30:70, 10:90, 0:100, w/w) were investigated. The ratios of WPI to SPI showed little effect on the WHC of the mixed protein emulsion gels (p > 0.05). Increasing the ratio of SPI decreased the hardness and storage modulus (G′) of mixed protein emulsion gels, whereas the porosity of mixed protein emulsion gels in the microstructure increased, as shown by CLSM. Both β-lactoglobulin and α-lactalbumin from WPI and 7 S and 11 S from SPI participated in forming the gel matrix of mixed protein emulsion gels. More protein aggregates existed as the gel matrix filler at the high soy protein levels. Interestingly, the G′ of mixed protein emulsion gels at the WPI to SPI ratio of 50:50 was higher than the sum of G′ of individual WPI and SPI emulsion gels. The whey protein network predominated the gel matrix, while soy protein predominated in the active filling effect. When subjected to an in vitro dynamic gastric digestion model, soy protein in the gels (WPI:SPI = 50:50) degraded faster than whey protein during gastric digestion. This study provided new information on the characteristics of composite protein emulsion gel fabricated with the WPI and SPI mixture.

Unraveling the potential health impact of the interactions between pea hydrolysates/peptides originating under gastric digestion and bile salts

Bile salts (BS) are biological surfactants that have important physiological functions mainly by participating in lipid digestion and intervening in the transport, absorption, and excretion of hydrophobic products. Bile salts have been shown to interact with the products of protein hydrolysis, being this interaction a key point to modulate several physiological processes.The type and size of peptides, released at different times of gastric digestion, could have different implications in these physiological processes modulated by the BS. In the present study we focused on understanding how the interactions of hydrolysates/peptides from native or commercial pea protein isolates with BS (formation of insoluble complexes or the modification of the BS micellar solubilization of poorly soluble molecules) evolve according to their residence time in a static gastric digestion model. The different residence times (10–60 min) would simulate different emptying points in which the partially hydrolyzed pea proteins by pepsin in the stomach are flushed into the duodenum and come into contact with the BS.It is observed that the longer residence times in the stomach the degree of hydrolysis of the pea isolates is greater, producing an increase in the soluble fraction. Both isolates showed a slight tendency to bind BS and form insoluble precipitates. The interaction of the soluble fraction of pea protein hydrolysates with the BS micelles, acted synergistically, increasing the solubilization capacity of oleic acid, taken as a model molecule.Likewise, it is shown that the structural changes of pea proteins due to processing have a profound influence on the interaction with BS and potentially affect the physiological reactions that they modulate.

Interplay of egg white gel pH and intragastric pH: Impact on breakdown kinetics and mass transport processes

Egg white gels have been utilized as a model system to study protein breakdown kinetics based on physical and biochemical breakdown processes during in vitro gastric digestion. Additionally, the impact of regulating intragastric pH on the breakdown kinetic processes was investigated. The present study evaluated the impact of gel pH (based on the pH of protein dispersion prepared at pH 3, 5 and 7.5) and intragastric pH regulation (with or without adjustment to pH 2 during in vitro gastric digestion) on the effective diffusion of gastric juice components (water and HCl), gel softening kinetics during gastric digestion, microstructural analysis using micro- computed tomography and protein hydrolysis in the liquid and solid fraction of egg white gel digesta. Egg white gels were subjected to 30 s oral digestion and 15, 30, 60, 120, 180 or 240 min gastric digestion in a static in vitro gastric digestion model, with or without gastric pH adjustment to pH 2. The gel pH affected all the properties measured during gastric digestion and each gel pH represented a specific driving mechanism for protein breakdown. A lower gel pH (pH 3) demonstrated a higher diffusion of moisture and acid, resulting in faster softening (p < 0.05). An intermediate pH (pH 5) showed greater protein–protein interactions due to the proximity to the isoelectric point of egg white proteins, resulting in very slow softening during digestion (p < 0.05), and a higher pH (pH 7) resulted in higher acid diffusion, intermediate gel hardness and very slow softening kinetics (p < 0.05). The gastric pH adjustment during digestion of egg protein gels affected (p < 0.05) the equilibrium moisture and acid contents as well as protein hydrolysis. The study confirmed that there is an interplay between initial gel pH and the intragastric pH which affected the breakdown kinetics of egg white gels during the gastric digestion process.

Characterization and Genomic Analysis of a New Phage Infecting Helicobacter pylori.

Helicobacter pylori, a significant human gastric pathogen, has been demonstrating increased antibiotic resistance, causing difficulties in infection treatment. It is therefore important to develop alternatives or complementary approaches to antibiotics to tackle H. pylori infections, and (bacterio)phages have proven to be effective antibacterial agents. In this work, prophage isolation was attempted using H. pylori strains and UV radiation. One phage was isolated and further characterized to assess potential phage-inspired therapeutic alternatives to H. pylori infections. HPy1R is a new podovirus prophage with a genome length of 31,162 bp, 37.1% GC, encoding 36 predicted proteins, of which 17 were identified as structural. Phage particles remained stable at 37 °C, from pH 3 to 11, for 24 h in standard assays. Moreover, when submitted to an in vitro gastric digestion model, only a small decrease was observed in the gastric phase, suggesting that it is adapted to the gastric tract environment. Together with its other characteristics, its capability to suppress H. pylori population levels for up to 24 h post-infection at multiplicities of infection of 0.01, 0.1, and 1 suggests that this newly isolated phage is a potential candidate for phage therapy in the absence of strictly lytic phages.

Dynamic in vitro gastric digestion behavior of goat milk: Effects of homogenization and heat treatments

The gastric digestion behavior of differently processed goat milks was investigated using a dynamic in vitro gastric digestion model, the human gastric simulator. Homogenization and heat treatment of goat milk resulted in gastric clots with highly fragmented structures. They also delayed the pH reduction during digestion, altered the chemical composition of the clots and the emptied digesta, promoted the release of calcium from the clots, and accelerated the hydrolysis and the emptying of milk proteins. The apparent density of the protein particles and the location of the homogenized fat globules changed during the digestion process, as shown in the emptied digesta of the homogenized goat milks. The effects of processing on the digestion behavior of goat milk were broadly similar to those previously reported for cow milk. However, the overall gastric digestion process of goat milk was more affected by homogenization than by heat treatments.

Antiglycating Effect of Phenolics from the Chilean Currant Ribes cucullatum under Thermal Treatment.

Numerous dietary polyphenols possess antiglicating activity, but the effects of thermal treatment on this activity are mostly unknown. The effect of thermal treatment in the antiglycating activity of polyphenolic enriched extracts (PEEs) from Ribes cucullatum towards glyoxal-induced glycation of sarcoplasmic proteins was assessed. Sarcoplasmic proteins from chicken, beef, salmon, and turkey, were incubated 2 h at 60 °C with and without glyoxal and different concentrations of PEEs (0.25, 0.5, 1, and 5 mg/mL). The antiglycating activity was evaluated by: (1) Lys and Arg consumption, (2) Carboxymethyl lysine (CML) generation, and (3) lipid-derived electrophiles inhibition in a gastric digestion model. Protective effects were observed against CML generation in proteins and a decrease of electrophiles in the gastric digestion model. A dose-dependent consumption of Lys and Arg in proteins/PEEs samples, indicated the possible occurrence of quinoproteins generation from the phenolics. Protein/PEEs incubations were assessed by: (1) High pressure liquid chromatography analysis, (2) Gel electrophoresis (SDS-PAGE), and (3) Redox cycling staining of quinoproteins. Protein/PEEs incubations produced: (1) Decrease in phenolics, (2) increase of protein crosslinking, and (3) dose-dependent generation of quinoproteins. We demonstrate that phenolic compounds from R. cucullatum under thermal treatment act as antiglycating agents, but oxidative reactions occurs at high concentrations, generating protein crosslinking and quinoproteins.

Formulation development of a live attenuated human rotavirus (RV3-BB) vaccine candidate for use in low- and middle-income countries

ABSTRACT Formulation development was performed with the live, attenuated, human neonatal rotavirus vaccine candidate (RV3-BB) with three main objectives to facilitate use in low- and middle- income countries including (1) a liquid, 2–8°C stable vaccine, (2) no necessity for pre-neutralization of gastric acid prior to oral administration of a small-volume dose, and (3) a low-cost vaccine dosage form. Implementation of a high-throughput RT-qPCR viral infectivity assay for RV3-BB, which correlated well with traditional FFA assays in terms of monitoring RV3-BB stability profiles, enabled more rapid and comprehensive formulation development studies. A wide variety of different classes and types of pharmaceutical excipients were screened for their ability to stabilize RV3-BB during exposure to elevated temperatures, freeze-thaw and agitation stresses. Sucrose (50–60% w/v), PEG-3350, and a solution pH of 7.8 were selected as promising stabilizers. Using a combination of an in vitro gastric digestion model (to mimic oral delivery conditions) and accelerated storage stability studies, several buffering agents (e.g., succinate, adipate and acetate at ~200 to 400 mM) were shown to protect RV3-BB under acidic conditions, and at the same time, minimize virus destabilization during storage. Several optimized RV3-BB candidate formulations were identified based on negligible viral infectivity losses during storage at 2–8°C and −20°C for up to 12 months, as well as by relative stability comparisons at 15°C and 25°C (up to 12 and 3 months, respectively). These RV3-BB stability results are discussed in the context of stability profiles of other rotavirus serotypes as well as future RV3-BB formulation development activities.

Phenolic composition, antioxidant capacity and α-glucosidase inhibitory activity of raw and boiled Chilean Araucaria araucana kernels

The Araucaria araucana kernels are a traditional food in southern Chile and Argentina. The aim of this work was to determine the composition of the phenolic-enriched extracts (PEEs) of the boiled kernels as well as their antioxidant capacity, inhibitory activity on metabolic syndrome-associated enzymes and effect on postprandial oxidative stress in a simulated gastric digestion model. The PEEs composition was assessed by HPLC-DAD-MS/MS. The main PEEs constituents were catechin and epicatechin in the unbound form, while hydroxybenzoic acids occurred mainly in the bound form. The unbound phenolics from boiled kernels showed significant correlations with DPPH, FRAP, TEAC (Pearson’s r of 0.481, 0.331 and 0.417, respectively) and lipid peroxidation (r = 0.381) and were more active than the bound phenolics. The extracts were highly active against α-glucosidase (IC50: 0.33–3.15 µg/mL) and reduced lipoperoxidation. Traditional processing increases the flavan-3-ol content. Our results suggest that this traditional food has potential health promoting properties.

A semi dynamic in vitro digestion study of milk protein concentrate dispersions structured with different polysaccharides

Hydrocolloids are often added as functional ingredients in foods, to better design the structure of the matrix and ensure food quality and optimal sensory properties. However, much less is known about their influence on the physical and chemical changes during gastric digestion. In this study, semi-continuous in vitro gastric digestion was applied on a model food system, prepared with milk protein concentrate (MPC) (3% w/v) and 1% alginate, pectin, guar gum, as well as a 1:1 mixture of alginate and pectin. The dynamics during simulated gastric digestion were observed by measuring particle size distributions, structuring at various length scales, as well as by evaluating differences in protein breakdown. Immediately after contact with the simulated gastric fluids, all samples showed extensive aggregation and formation of different structures. MPC control dispersions (no polysaccharide) and MPC containing alginate formed large inhomogeneous aggregates. The lack of structural homogeneity affected the simulated gastric emptying: there were marked differences in the type of aggregates present at various times of emptying depending on the hydrocolloid present in the mixture. MPC containing pectin or guar gum formed macroscopically homogeneous dispersion, with rather small protein aggregates showing a large population of particles between 60 and 100 ​μm of diameter, with marked differences in microstructure. Pectin created large coacervates, while guar microscopic phase separated systems. These dispersions showed a higher extent of protein digestion, due to the larger surface area created for enzyme activity compared to the macroscopically phase separated matrices. In all cases, there was a large undigested fraction at the end point of 140 ​min. SDS PAGE demonstrated differences in the casein peptides distribution depending on the type of polysaccharide present during simulated gastric emptying. This in spite of similarities in cumulative protein emptied. It was concluded that in this semi-continuous in vitro gastric digestion model, structuring with polysaccharides has a significant impact on gastric emptying and protein digestion kinetics.

Preformulation Characterization and Stability Assessments of Secretory IgA Monoclonal Antibodies as Potential Candidates for Passive Immunization by Oral Administration.

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrheal disease among children in developing countries, and there are no licensed vaccines to protect against ETEC. Passive immunization by oral delivery of ETEC-specific secretory IgAs (sIgAs) could potentially provide an alternative approach for protection in targeted populations. In this study, a series of physiochemical techniques and an in vitro gastric digestion model were used to characterize and compare key structural attributes and stability profiles of 3 anti–heat-labile enterotoxin mAbs (sIgA1, sIgA2, and IgG1 produced in CHO cells). The mAbs were evaluated in terms of primary structure, N-linked glycan profiles, size and aggregate content, relative apparent solubility, conformational stability, and in vitro antigen binding. Compared to IgG1 mAb, sIgA1 and sIgA2 mAbs showed increased sample heterogeneity, especially in terms of N-glycan composition and the presence of higher molecular weight species. The sIgA mAbs showed overall better physical stability and were more resistant to loss of antigen binding activity during incubation at low pH, 37°C with pepsin. These results are discussed in terms of future challenges to design stable, low-cost formulations of sIgA mAbs as an oral supplement for passive immunization to protect against enteric diseases in the developing world.

Development and validation of a new artificial gastric digestive system.

The stomach is a major digestive organ of the human body that plays a role in storing, mixing, reducing chylous particles and breaking down ingested foods. This study established a new artificial gastric digestive system (AGDS) with a human stomach shape and structure by a 3D digital technology. Two sets of symmetrical rollers and one set of contrary movement of the roller were used to simulate the peristalsis of the stomach, and a pH-stat workstation was applied to control the pH. The force, pepsin and gastric juice secretion, gastric emptying and pH changes of AGDS were tacked and validated. Besides, the digestion behavior of α-lactalbumin using AGDS model, static model and semi-dynamic model (pH and enzyme changes) were studied. The results showed that the hydrolysis and morphology of protein, peptide and amino acids accumulation obtained by AGDS were different from the static digestion and semi-dynamic digestion models, indicating pH and gastric motility had certain effect on protein hydrolysis, particularly in the pepsin activity changes at early stage of digestion. AGDS, verified by mechanical analysis and in vitro digestion experiments, indicated that it can provide α-LA protein solution with a true and reliable digestion profile in the stomach, and can be used as a potential dynamic gastric digestion model for the food development.

Flocculation of oil-in-water emulsions stabilised by milk protein ingredients under gastric conditions: Impact on in vitro intestinal lipid digestion

The effect of the gastric behaviour of protein-stabilised oil-in-water emulsions on intestinal lipid digestion was investigated using an in vitro dynamic gastric digestion model ‒ the human gastric simulator (HGS) and an intestinal model. Emulsions were prepared using milk protein concentrate (MPC), calcium-depleted MPC or sodium caseinate. In the MPC-stabilised emulsion, flocculation, induced by the milk-clotting enzyme pepsin, occurred after 10 min of digestion (at pH > 6) in the HGS. Closely knitted flocs of large size, which remained in the HGS throughout the gastric digestion, were formed. However, in emulsions stabilised by calcium-depleted MPC or sodium caseinate, flocculation occurred after approximately 40 min of digestion because of the low pH (∼pH 5); the flocs were relatively small and disintegrated after further digestion. The particle sizes of the gastric digesta mixtures obtained at each digestion time were in the order: MPC emulsion > calcium-depleted MPC emulsion > sodium caseinate emulsion. In contrast, the oil contents of the mixtures were in the order: MPC emulsion < calcium-depleted MPC emulsion < sodium caseinate emulsion, suggesting that the MPC emulsion had a slower release of oil droplets into the intestine than the calcium-depleted MPC and sodium caseinate emulsions. In the intestinal phase, the extent of lipid digestion followed the order: MPC emulsion < calcium-depleted MPC emulsion ≤ sodium caseinate emulsion. The results suggested that the structures and the size of the flocs induced by interactions between milk proteins and pepsin or acid during the gastric digestion of emulsions influence intestinal lipid digestion.

Texture changes and protein hydrolysis in different cheeses under simulated gastric environment

The structure of food plays an important role in determining rate of digestion by influencing the disintegration rate and affecting the release of bioaccessible components. In the stomach, breakdown of food structure occurs through mechanical peristaltic forces and hydrolysis of macronutrients. The objective of this study was to investigate the gastric digestion of Cheddar, Mozzarella, and Parmesan cheeses using both static soaking method and dynamic in vitro gastric digestion model. During static soaking in simulated gastric juice, cheeses had less texture softening at lower pH. Mozzarella cheese showed texture hardening behavior, leading to the lowest rate of nutrient leaching among the three cheeses, while Parmesan cheese had the highest rate of nutrient leaching. During dynamic gastric simulation, Mozzarella cheese showed the most resistance to protein hydrolysis by generating only 6.81 g/L amino acids when compared to 12.70 g/L and 24.3 g/L amino acids released by Cheddar and Parmesan cheese, respectively. The resistance of Mozzarella cheese was attributed to the dense outside layer formed due to aggregation of the protein matrix at highly acidic environment that encapsulated the cheese particles and prevented gastric juice from further digesting the proteins.

Formulating orange oil-in-water beverage emulsions for effective delivery of bioactives: Improvements in chemical stability, antioxidant activity and gastrointestinal fate of lycopene using carrier oils

The influence of carrier oil type on the chemical stability, antioxidant properties and bioaccessibility of lycopene in orange oil-in-water beverage emulsions was investigated. The emulsions were formulated with orange oil (A), which was partially (50%) replaced with tributyrin (B) or corn oil (C) because of their distinctively different fatty acid composition. The addition of corn oil enhanced the physical stability of the beverage during chilled storage by inhibiting Ostwald ripening. The formation of oxidation products was insignificant after storage for 28 days at 4 °C, regardless the type of added oil. Lycopene was more susceptible to chemical degradation in the presence of unsaturated, long chain triglycerides and the retention followed the order: A (87.94%), B (64.41%) and C (57.39%). Interestingly, bioaccessibility of lycopene was significantly lower for emulsions formulated with 50% corn oil as opposed to 100% orange oil as indicated by the simulated in vitro gastric digestion model.

Dairy food structures influence the rates of nutrient digestion through different in vitro gastric behaviour

The purpose of this study was to investigate in vitro the extent to which specific food structures alter gastric behaviour and could therefore impact on nutrient delivery and digestion in the small intestine. Results obtained from a specifically developed gastric digestion model, were compared to results from a previous human study on the same foods. The semi-dynamic model could simulate the main gastric dynamics including gradual acidification, lipolysis, proteolysis and emptying. Two dairy-based foods with the same caloric content but different structure were studied. The semi-solid meal comprised a mixture of cheese and yogurt and the liquid meal was an oil in water emulsion stabilised by milk proteins. Our findings showed similar gastric behaviour to that seen previously in vivo. Gastric behaviour was affected by the initial structure with creaming and sedimentation observed in the case of liquid and semi-solid samples, respectively. Lipid and protein digestion profiles showed clear differences in the amount of nutrients reaching the simulated small intestine and, consequently, the likely bioaccessibility after digestion. The semi-solid sample generated higher nutrient released into the small intestine at an early stage of digestion whereas nutrient accessibility from liquid sample was delayed due to the formation of a cream layer in the gastric phase. This shows the strong effect of the matrix on gastric behaviour, proteolysis and lipolysis, which explains the differences in physiological responses seen previously with these systems in terms of fullness and satiety.

Pepsin-like protease activity and the gastric digestion within ex vivo Pacific bluefin tuna Thunnus orientalis stomachs, as a gastric digestion model

Isolated whole stomachs of farmed Pacific bluefin tuna Thunnus orientalis were externally batch-cultured in cell culture medium at 24°C for 8h. This was done in order to confirm that gastric function was maintained during incubation (Exp. 1) so that the effectiveness of the ex vivo technique outlined in the present study in serving as an artificial method of gastric digestion could be determined (Exp. 2). During experiment 1, fresh or cold-stored stomachs (48h on ice) were intra-gastrically infused with a saline solution (control group) or a skipjack tuna broth stimulant (infusion group). Pepsin-like protease activities within the gastric effluent of each study group were compared. In both control and infusion groups, fresh stomachs demonstrated higher pepsin-like protease activity. Within fresh stomachs, protease activity subsequent to stimulant infusion was significantly greater than it was in the control group. In cold-stored stomachs, however, no difference was observed in the protease activities of control and infusion groups. According to the results, fresh stomachs respond to luminal stimuli. Furthermore, fresh stomachs exhibited motility during incubation while cold-stored stomachs did not. Mucosal layers within fresh stomachs indicated histological normality subsequent to incubation. In experiment 2, both fresh and cold-stored stomachs were filled with a diet consisting of boiled fish paste. After a period of 8h, dry matter loss of diet was significantly greater within fresh stomachs than it was in cold-stored stomachs. The level of pepsin-like protease activity within fresh stomachs was also higher than levels observed within cold-stored stomachs during the incubation period. These results suggest that fresh stomachs obtained from bluefin tuna maintained functionality ex vivo and that the technique outlined in the present study could be used effectively in the evaluation of bluefin tuna gastric digestion.

Effect of carnosic acid, quercetin and α-tocopherol on lipid and protein oxidation in an in vitro simulated gastric digestion model

Carnosic acid, quercetin and α-tocopherol are well-known antioxidants in many biological systems. However, their antioxidative effect during food digestion against lipid and protein oxidation is not well known. Therefore, in this study, an in vitro simulated gastric digestion model was used to investigate their stability during gastrointestinal conditions and their antioxidative properties during low pH digestion. In general, the stability of the antioxidants in the different steps of digestion was in the order of α-tocopherol > quercetin > carnosic acid. Salivary components, as well as the acidity of the gastric juice, were responsible for the reduction in antioxidants. Both α-tocopherol and quercetin were able to lower lipid oxidation during digestion, while the effect on protein oxidation was not clear. In contrast, carnosic acid did not have any effect on lipid oxidation and tended to stimulate protein oxidation. This study clearly demonstrated that the environmental conditions are of major importance to the properties of antioxidant compounds.